1. Field
Various examples described herein relate generally to writing magnetic servo patterns to magnetic storage media, and in one aspect to position detection and servo writing control methods and systems for writing a servo track or pattern to a magnetic storage medium.
2. Related Art
Digital data-recording on tape remains a viable solution for storage of large amounts of data. Conventionally, at least two approaches are employed for recording digital information onto magnetic or optical recording tape. One approach calls for moving a recording medium past a rotating head structure that reads and writes user information from discontinuous transverse tracks. Interactive servo systems are typically employed to synchronize rotation of the head structure with travel of the medium. This method is generally referred to as “Helical Recording.” Another approach is to draw the recording medium across a non-rotating head at a considerable linear velocity. This approach is sometimes referred to as longitudinal recording and playback.
Increased data storage capacity, and retrieval performance, is desired of all commercially viable mass storage devices and media. In the case of linear tape recording a popular trend is toward multi-channel movable head structures with narrowed recording track widths and read track widths so that many linear data tracks may be achieved on a recording medium of a predetermined width, such as one-half inch width tape. To increase the storage density for a given cartridge size the bits on the medium may be written to smaller areas and on a plurality of parallel longitudinal tracks.
In multi-head, multi-channel magnetic tape storage systems, random lateral tape motion (“LTM”) is generally a limiting factor in achieving higher track densities and thus higher user data capacity per tape. In order to maintain proper alignment of the head with the storage tape and data tracks on the tape, the tape is generally mechanically constrained to minimize LTM and data retrieval errors. Misregistration between the head and the data track can cause data errors during readback and data loss on adjacent tracks during writing.
Various techniques for increasing the track density on magnetic tape employ recording servo information on the tape to provide positioning information to a tape drive system during writing and/or reading processes. Some systems magnetically record a continuous track of servo information which is then read and used as a position reference signal. For example, a variety of techniques have been used including dedicated and embedded magnetic servo tracks, time and amplitude magnetic servo tracks, and the like. Other systems may intersperse or embed servo information with user data. Exemplary tape drive systems and methods are described, for example, in U.S. Pat. Nos. 6,246,535, 6,108,159, 5,371,638, and 5,689,384, all of which are hereby incorporated by reference herein in their entirety.
Additionally, LTM is an important factor in the performance of servo writers, which record the servo pattern to the magnetic storage medium. LTM during the servo writing process may result in undesired lateral pattern motion (“LPM”) of the servo pattern. LPM of the servo pattern generally has a detrimental effect on servo performance of the magnetic storage medium. Accordingly, LTM is generally minimized by controlling the path of the magnetic storage medium during the servo writing process; however, increased control of the path generally increases the mechanical complexity of the servo writer.